Hydraulic pump or motor



March 16, 1965 J. HULMAN ETAL HYDRAULIC PUMP OR MOTOR 4 Sheets-Sheet 1 Filed March 21, 1957 I a v INVENTORS HULMMI By 9148 lffqe zr M52 w W March 16, 1965 J. HULMAN ETAL 3,173,376

HYDRAULIC PUMP OR MOTOR Filed March 21, 1957 4 Sheets-Sheet 5 3 J 2- i Q $3 "g; i? INVENTORS uauus HULMAN BERNARD BEAMAN i Max mucso/v MCTW March 16, 1965 J. HULMAN ETAL HYDRAULIC PUMP OR MOTOR 4 Sheets-Sheet 4 Filed March 21. 1957 United States Patent 3,173,376 HYDRAULIC PUMP QR MGTOR Julius Hulrnan, Bernard Beanran, and Max Isaacson, Dayton, Ohio, assignors to United Systems Corporation, a corporation of Qhio Filed Mar. 21, 1957, Ser. No. 647,614 Claims. or. 103-162) This invention relates to a piston type hydraulic pump or motor and more particularly to a pump or motor of the rotating cylinder-barrel type in which a thrust or swash plate engages one end of the piston or piston rods to receive thrust forces thereon.

This application is a continuation-in-part of application number 495,548, filed March 21, 1955, now abandoned.

In a pump or motor of this type, the reciprocation of the pistons is accomplished by thrusting one end of the piston assemblies against an inclined thrust member. This thrust member is usually free to rotate on its inclined axis and is in the form of a plate. It has been suggested that this can be accomplished by inserting an additional member in the housing, which is machined at an angle to the axis of the housing so as to form a seat for the thrust member. Also, various other types of machining procedures were previously used for forming a seat for the thrust plate, wherein the thrust and housing axes are parallel or coincident. Such structural arrangements, in combination with retention of the pistons, have resulted in bulky or costly designs.

In pumps or motors of this type it is desirable that the rapidly reciprocating pistons or piston rods be firmly and snugly held against the thrust member at all times. This is particularly important in order to prevent loss of fluid through the piston rod (if hollowed rods are used) to avoid scoring and erosion of the thrust surfaces and reduce or eliminate high dynamic loads which may initiate destructive stresses in piston members. During a portion of the operating cycle the resultant forces due to pressure on the piston and inertia, are such as to cause or tend to cause the piston to leave the thrust member or plate. This can be overcome by applying adequate charging pressure in the case of a pump, or back or discharge pressure in the case of a motor. This, however, causes undue penalty to performance by reducing the torque efficiency. Various other methods have been employed to provide continuous piston-to-thrust member retention, the most common one being the use of springs which bear directly or indirectly on a fixed portion of the housing and load another hold-down member or assembly against the piston rods. In view of the resilient nature of the retention means, such devices are subject to resonant vibration response, or the size and weight of the spring becomes prohibitively large to prevent piston thrust face unseating at high speeds, thus seriously limiting high speed performance.

The use of flat bearing surfaces to carry high thrust loads is a common expedient. In the case of rotatingbarrel-type pumps and motors, attempts have been made 'to hydraulically balance the rotating thrust member against the stationary back-up or support surface. Such balancing has been, at best, intermittent and ineffectual since the communication of fluid under pressure to the interface between the thrust member and'its support has not been substantially continuous, but has been dependent upon the registration of portions of a communicating passageway, wherein even at registration only an ineffectual hydraulic force is transmitted so that no substantial balancing occurs.

In the case of the balancing of the piston thrust against the thrust member at the interface of the thrust member and the piston rods or shoes, many arrangements have been suggested. Means have been employed which are 3,173,376 Patented Mar. 16, 1965 based on the principle that substantial balancing and even overbalancing should be obtained (i.e. a counter piston thrust force is developed substantially equal to or greater than the piston thrust force) which can be satisfactorily maintained for all or most conditions of operation. Generally, two factors have been considered in establishing hydraulic balancing, i.e., area and pressure.

The piston and piston rods or shoes have been provided with interconnecting passages leading to a recess in the piston shoes at their thrust plate engaging surfaces. The size of the recesses in the piston rods at their thrust plate engaging surface in relation to the area of the head end of the piston, is one factor in establishing balance. The second factor is the pressure exerted by the fluid within the piston shoe recesses. By proper correlation of the head end piston area with the effective area on the thrust side of the piston, a counter or opposing piston thrust (i.e. an anti-piston force) force is developed to counteract the thrust component of the prime force imposed by the fiuid on the head end of the piston. Previously, it has been suggested that full or substantially full pressure be exerted in the piston shoe recesses, i.e. the pressure in the shoe recesses is of the order of of the pressure exerted on the head end of the piston. This reduced pressure at the shoe recesses implies a flow. However, the nature of this flow, nor its significance have not been heretofore described. Also, the aforementioned area correlation has been such that, in combination with the pressure transmitted to the piston shoe recess, an antipiston force has been developed which is equal to or greater than the thrust component of the prime force at the head end of the piston. These two force relationships are hereinafter referred to as piston balance and piston over-balance, respectively.

Various structural arrangements have been devised to accomplish this objective of providing piston balance or piston over-balance to counteract the force transmitted to the pistons by the fluid being circulated in the pump or motor. In one such arrangement a hollow open-ended piston is employed with a passageway leading therefrom through a knuckle joint with the piston rod, and then through a connecting passage in the piston rod or shoe to the recess therein. In some instances the passage through the piston has been provided with a metering device, such as a rod extending through a bore in the piston, whereby an annular flow passageway is formed. Even in such constructions the passageways, shoe recess area and shoe contact area are so dimensioned as to obtain high rate of fluid fiow thereby maintaining full or substantially full fluid pressure in the recesses (as compared with the pressure at the head end of the piston) substantially at all times, and creating piston balance or overbalance.

Under the existing conditions of sliding motion and because of lack of hydrodynamic wedge action, similar to that which occurs in a journal and bearing to support the load, piston balance or over-balance can be maintained only by copious lubrication of the thrust faces. High pressure in the shoe recesses correlated with the projected shoe recess areas are therefore requirements to maintain a fluid flow at the interface. According to the prior art this has been maintained at the expense of high flow from the shoe recess with subsequent penalty of excessive loss in volumetric efiiciency.

In connection with a general consideration of providing a continuous copious lubricating film at the interface of a piston and its bearing surface in fluid pumps or motors, it is pertinent to consider a recent suggestion to employ a metering rod through the piston which is spring loaded and carries a valve member. In such a construction, the pressure in the shoe recess at the beginning of the pressure stroke is zero or case pressure. At the instant the pressure stroke begins (or in the case of suddenly applied loads) the shoe is forced against the thrust plate and a lubricating film is no longer present at the interface of the thrust member and piston shoe. Although the metering rod within'the piston permits a high pressure flow sulficient to maintain a lubricating film substantially throughout the entire length of the piston stroke, such how is not sulficiently rapid nor the pressure build-up sufficient to instantaneously unseat the shoe from the thrust member and establish a lubricating film at the instant of the commencement of the high pressure stroke. In this aforesaid construction, at the commencement of the pressure stroke the spring loaded rod is axially moved to force fluid from the shoe recess to the interface of the bearing surfaces (i.e. break the seating of the-shoe). Thereafter, during the remainder of the' pressure stroke, high pressure fluid is transferred from the head end of the piston around the metering rod and through the piston rod passageway to the shoe recesses to provide the pressure necessary to maintain the lubricating film at the interface and maintain an overbalance.

It is therefore, an object of this invention to provide a simple and inexpensive method of fabricating a housing for a fluid pump or motor with an integral inclined surface for the thrust member. It is another object of this invention to provide simple means, without employing springs, for positively holding the pistons against the thrust member in a fluid pump or motor. It is still another object of this invention to provide means employing viscous flow for limiting leakage at the piston thrust member interface and consequent loss of volumetric efficiency even at high pressure, high temperature and high rotative speed, in a fluid pump or motor, independent of the degree or type of balancing of the piston shoe.

It is a further object of this invention to provide a simple means for balancing the freely rotating piston thrust member.

It is' a still further object'of this invention to provide a viscous flow path in a fluid pump or motor in a flow passageway leading from the head end of the piston to the piston shoe recess. Another object of the invention is to provide, within such viscous flow path, means for effecting a continuous wiping action on the walls thereof throughout the pressure stroke.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from a reading of the following description and drawings, in which:

FIGURE 1 is a side view of the pump or motor partially broken away to show the low pressure and high pressure ducts,

FIGURE 2 is a central cross sectional view of the pump or motor,

FIGURE 3 is a cross sectional view of the pump, taken on the line 3-3 of FIGURE 2,

FIGURE 4 is an enlarged cross-sectional view of a portion of the thrust package showing the piston arrangement of FIGURE 2,

FIGURE 5 is a cross-sectional View, taken on the line 55 of FIGURE 4,

FIGURE 6 is a fragmentary, cross-sectional view of a modification of the hydraulic balancing means of the thrust member,

FIGURE 7 is a fragmentary cross-sectional view of a modification of a portion of the hydraulic balancing means for the piston shoe,

FIGURE 8 is an exploded view of the thrust package,

FIGURE 9 is a cross-sectional view of the thrust package and piston rod assembly showing additional means for insuring a seating of the piston shoe on the thrust surface,

FIGURES l014 are cross-sectional views similar to FIGURE 9 and show further modifications of additional means for insuring a seating of the piston shoe on the thrust surface, and,

FIGURE 15 is a cross-sectional view similar to FIG- URE 9 showing alternate means for actuating the additional means shown in FIGURE 9.

In this invention novel means are employed based upon the modus operandi that irrespective of the condition of piston balance a viscous flow is provided, resulting in partial film lubrication at the interface of the piston shoe and thrust member with maximum sealing against seepage from the shoe recess. This viscous flow is obtained by an impedance path formed in the passageway leading to the shoe recess by having a portion of a capillary nature, i.e. of a dimension such as to limit flow to a laminar or viscous character. The character of flow of fluids in closed members such as pipes is readily and precisely defined by the well known dimensionless parameter, Reynolds number:

D conduit internal diameter or characteristic length A certain critical value of the Reynolds number, defines the transition point or lower limit of a transition range between laminar flow and turbulent flow. The velocity corresponding to this critical value N is termed the critical velocity. Thus, for a passage of given equivalent diameter and carrying a fluid of a certain viscosity, the fluid flow is laminar if the actual average velocity is below the critical velocity. As the velocity is increased (higher Reynolds number) the character of the flow changes to turbulent flow. The change from laminar to turbulent is not instantaneous but occurs gradually over a range of values of Reynolds numbers known as the transition range. In practice, in the case of a fluid pump or motor, a capillary passageway may be readily obtained and easily controlled dimensionally by using the clearance path between the piston and bore. This constitutes a capillary annular type opening and the associated equivalent diameter applied to the Reynolds number calculation is or" such magnitude as to limit the velocity of fluid flow induced under the influence of even very high fluid pressures to suiliciently low values so as to retain the character of laminar type flow.

Under conditions of perfect sealing between the thrust and piston shoe members, there is no leakage therebetween, and static conditions prevail. In such event regardless of the viscous restriction in the passageway, under the condition of perfect sealing and in the course of time, full pressure will be transmitted to the recess in the shoe face from the head end of the piston. Should the shoe unseat momentarily (as occurs during actual operation, because of variations in the friction coeflicicnt between the sliding surfaces), and if a capillary passage is employed, the flow is nevertheless limited to the laminar region by the capillary area as described above. Under this condition, very low pressures, of the order of that existing in the case or housing will occur in the shoe recess, and a high unbalanced thrust force is available to again substantially resent the piston shoe. The shoe recess pressures will be restored, but at a relatively slow rate in view of the low fiuid velocity and time thereby required. The shoes will therefore alternately seat and then unseat, thereby producing a varying or pulsating pressure in the shoe recess. Under given constant conditions of operation of the fluid motor or pump, such as speed, inlet and outlet pressures, temperature and fluid, the above mentioned pulsating or pressure cycling will exist within the shoe recess. The result will be to produce some reduced average pressure in the shoe recess. This average pressure" will be materially lower ihun the fluid pressure on the headcnd of the piston. Although leakage flow is limited to an acceptable value consistent with good volumetric efliciency, enough fluid for adequate partial lubrication of the thrust faces is available at all times to maintain intermittent metal-to-metal contact of the shoes with the thrust surface. The net result of the above is to provide a minimum of leakage with the capability of operation at speed-load factors appreciably above those heretofore considered possible.

According to the invention the inclined surface for the thrust member is provided by making the housing in two sections which are cut on a bias and in which the plane of the interface between the housing sections is parallel to the plane of the thrust surface. Also a thrust package or assembly is mounted within one housing section and due to the bias relationship, the mating section aids in maintaining the thrust package in position. The thrust package provides a positive retaining means for the piston rods.

The apparatus of the invention also provides a balance for the thrust member at the interface with its support member by means of a plurality of passages and recesses in the thrust member adapted to be in registry with the piston shoe recesses and wherein the number of piston shoes and thrust plate passages are so correlated as to obtain a constant or substantially constant balancing of the thrust plate.

Referring particularly to FIGURES l and 2, the numeral generally designates a hydraulic pump or motor. The hydraulic pump or motor comprises a housing which is formed in two parts, namely, the flange housing 12 and the barrel housing 14. Depending upon whether the device is used as a pump or motor, a drive or driven shaft 16 is shown splined to the shaft 18, as at 2%. The shaft 18 is rotatably supported in the flange housing 12 by ball or roller bearings 22 and 29. The bearing 22 is locked in position against a shoulder on the shaft 18 on the one side and locked in position on the other side by any suitable locking means, such as a seal cage retainer 26 and a snap ring or the like 28. This arrangement holds the shafts 16 and 18 in concentric relationship with the flange housing 12. The other end of the shaft 18 is supported by roller bearing 29, mounted in cap 163.

The barrel housing portion 14 is provided with a cap 163. The housings 12 and 14 and the cap 163 are held together by bolts 46, also serving as dowels to properly align the assembly.

The barrel housing 14 is provided with a substantially cylindrical bore or cavity 14a, in which is contained a cylinder barrel 58.

The cylindrical barrel has internal splines 63 which mate with external splines 61 on the shaft 18.

A spring 18a is mounted upon the tapered end of the shaft 18 and engages a shoulder on the shaft. Spring washers 181) located in the bore at the outer end of the barrel 58, abut the opposite end of the spring 18a. This spring biases the barrel against the cap member 163.

The barrel 58 is provided with a plurality of cylindrical cavities, each receiving a piston assembly 42 (see FIG. 4). The piston assembly 42 includes a piston 52 that is provided with a spherical seat 53 receiving a ball of a connecting rod or shoe St). The spherical seat, together with the ball portion of the connecting rod 50, form a ball and socket joint. The connecting rod 50 terminates in a radially disposed flange portion Stia.

Referring to FIGURES 2 and 8, it will be seen that the connecting rod Stl thrusts upon the plate 38, which in turn thrusts upon plate 32, and in turn upon the housing surface 39. In addition, the connecting rod 50 is restrained by the hold-down plate 44, which is free for rotative movement in cage 36 and is in turn retained by cap 48. The action of these several members making up the thrust package will be more fully explained.

Suitable packing gaskets or O-rings are used in sealing the joint between members 12 and 14 and between member 14 and the cap 163. Suitable O-rings or sealing gaskets are also used in sealing the juncture between the inner race of the bearing 22 and the shaft 13. Other O-rings or sealing gaskets have been used, as clearly shown, where required.

In order to provide for easy manufacture and assembly of the pump, the pump or motor is comprised of a housing made of two parts, the flange housing 12 and barrel housing 14, whose mating surfaces are machined at an angle corresponding to the angle of the thrust plate. By having the parts machined at an angle as shown in FIG- URE 2, it is easy to machine a landor surface 30 for receiving a flat thrust package.

The thrust package is made up of flat pieces, all of which can be easily machined and measured to the required close limits of flatness and accuracy. The fit of the thrust package is easily maintained. This has been previously most difiicult and costly. The advantage of this type of thrust package is the ability to hold proper fits, tolerances and finishes. The thrust package is provided to take the pressure thrust of the piston which rotates with the barrel. In addition, the thrust package provides a means for retracting the piston on the filling stroke for the pump (emptying stroke for a motor). During the pressure stroke for a pump or a motor, the pressure forces the piston against the thrust plate. However, on the return stroke, if accomplished without pressure, the piston ball rod may tend to leave the thrust plate. Therefore, the retainer cap 48 which engages the retainer plate 44, which, in turn, engages the back faces of the ball rods, holds the pistons in their proper place and positively limits the permissable motion away from the plate. Further positive means for holding down the pistons are discussed hereinafter in connection with the description of FIGURES 9-15. Concentric with the land or surface 36 is a counterbore or the like 34 for receiving the thrust package, which includes a thrust plate cage 36 and a thrust plate 38. The thrust plate 38 is provided with a plurality of passageways or holes 40, which serve as a means for admitting the pressure of the fluid to the counterbores 41 on the other side of the thrust plate 38, so as to balance the forces thereon, further explanation of which will be hereinafter set forth.

The thrust plate cage 36 and the thrust plate 38 support a plurality of piston assemblies 42, best shown in FIGURE 4, which are held in position by a retainer or hold-down plate. The retainer plate is securely restrained by the barrel housing 14. It is noted that the barrel housing is machined on the same angle as shown at 43 as the flange housing 12. As shown in FIGURES l and 3, the flange housing 12 and the barrel housing 14 are held together and in proper alignment by four bolts 46. Again referring to FIGURE 4, it is noted that the inner diameter of the barrel housing 14 is smaller than the inner diameter of the flange housing, so as to provide a shoulder 47 for retaining the retainer plate 48 in place.

As more clearly shown in FIGURE 4, the piston assembly 42 comprises a flat faced connecting rod or shoe portion 50 and the piston 52. The retainer plate 44 is provided with openings for receiving the piston assembly 42. The openings 45 are sufliciently large to permit some play between the flat faced piston rods and retainer plate. The piston 52 is provided with a radially extending passageway 54 which communicates with an axially extending passageway 55. The passageway 55 enters into the spherical recess or seat 53 through a conical relief opening in the piston 52. Since the shoe also has a fluid passageway 50!) in communication with the passageway through a conical relief opening 55a, the flat face 57 of the shoe 50 is hydraulically connected to the radial passageway 54 in the piston 52. These passageways are of a diameter which offer no appreciable restriction in fluid flow. The conical relief openings in the piston and piston shoe permit relative movement of the parts While still hydraulically inter-connecting them. The passageway in the flat face 57 is counterbored to provide a recess, as shown at 59, so as to be in communication with the thrust passages 49 and recess 41 when the parts are in registry. Although a round counterbore 59 has been shown, any other shaped recess may be used.

herefore, the counterbore '41 may also be hydraulically connected to the radial bore 54 when the parts are in registry.

In order to obtain minimum leakage from the piston shoe recess, etc., there is interposed in the fiow passage a viscous path or flow limiting path such as L (see FIG- URE 4-), interconnecting the head end of the cylinder with transverse passageway 54 which restricts the flow to laminar and reduces the effective pressure maintained within the recess 59. This path L is of a capillary nature and may most advantageously be formed by the clearance between the piston and cylinder. In the modification shown in FIGURE 7 the path L takes the form of a long capillary passage 154 formed centrally of a piston 152 and extending from the head end of the piston to the ball and socket joint. However pressure communication by a leakage path past a portion of the piston is preferred since the capillary passage L is continually being wiped clean by the piston.

As the cylinder barrel 58 rotates, the openings in the barrel face index alternately with the slots in the cap 163. These slots communicate with the duct 64 and the duct 66 to supply and withdraw fluid from the cylinder barrel cavities.

As may best be seen by referring to FIGURE 4, the upper end of the cylindrical cavity is counterbored at 60 to provide a relief for the piston at its forward extremity of travel and for ease of fabrication of the piston bore. This counterbore, however, does not come in contact with the transverse passageway 54 when the piston 52 projects into the extreme inner position in the inner cylindrical cavity in the barrel.

The thrust plate 38 is not mechanically linked or tied to the pistons; but, rather, is freely floating in the thrust plate cage 36. It acts normally as a slip plate, preferably rotating at half barrel speed. In order to prevent a high pressure leak through the bores 40, and in order to insure a constant hydraulic balance of the thrust plate, the number of transfer holes 46 must be greater than the number of piston assemblies. Best results are obtained when the distance between the centers of adjacent bores 49 in the thrust plate 38 is slightly greater than the diameter of the recess or counterbore 59 in the flat face piston rod riding on the thrust plate. The arrangement of the holes 40 with respect to the piston rod face is such that at no time is there any possibility of a high pressure leak. In order to obtain the minimum acceptable substantially constant hydraulic balance between the thrust member and its supporting surface, the number of bores 46 must exceed the number of piston rods so that at least one rod and one bore 4% are in registry for any given relative displacement of the rod on the thrust plate which is less than the distance between the rod cavities of two adjacent piston rods. The number of bores 49 can of course be increased, if desired, so that all of the piston rod passages 5012 are each in registry with a bore 4 for all relative displacements of the rods on the thrust plate. This would be the optimum condition. As an alternative construction the plate 38 may be balanced by fluid conducted to a cavity at the interface of plate 38 and plateSZ; the fluid being conducted through a passageway extending through the housing, around the pistons and thrust package, and leading through plate 32 to the said cavity.

The thrust plate may be referred to as a slip plate, in that in the use of the device, whether it is as a pump or as a motor, the plate 38 tends to move in the direction of the path of the connecting rods. The pressure of the fluid in the recesses or cavitier 41 and cavities 59 is a function of the fluid pressure supplied to the pistons and the restriction interposed by the viscous flow path. The separating force due to the effective pressure in the cavity 59 is such that it is less than, but not much less than, the force exerted by the connecting rod against the thrust plate 38. However, the average pressure exerted within the recess or cavity 59 is appreciably less than the pressure exerted on the head end of the piston. The difference in the force exerted by the pressure in the cavity or counterbore 59 upon the end of the connecting rod and the thrust of the connecting rod against the plate 33 must be sufiicient to provide a seal at the interface between the connecting rod and the thrust plate 38 while still permitting partial lubrication of this interface. If the force exerted by the pressure of the fluid in the cavity 59 is too great, it will unseat the end of the connecting rod from the thrust plate 38, thereby permitting fluid to squirt out and not be retained in the cavity. Excessive leakage is prevented by virtue of the capillary restriction path in the communicating passageways.

The size of the recesses 41 may be any desired dimension since the relationship of the elements 32 and 38 is that of two flat sliding surfaces and the problem of holding a smaller rod on a plate (e.g. such as exists at the piston rod thrust plate interface) is not present. Hence any degree of balance can be attained at plate 38. However, the force exerted by the fluid in the recess 41 should be suflicient to reduce the friction between the thrust plate 38 and the plate32 to a suitable minimum, and still maintain seal. Minimum leakage at all times is again obtained because of the aforementioned capillary restriction.

By this arrangement, the device operates smoothly and the hydraulic balancing reduces wear of parts and greatly reduces hammering effects between the parts. When the pistons operate through the return stroke (while there is no pressure, or practically no pressure against the pistons or, at times there may be a suction), there is a tendency to pull the pistons into their cylinders and unseat the connecting rod from the plate 38. In order to limit this, the retainer plate 44, abutting the plate 48, engages the back surface of the radial flange 50a, so as to hold the connecting rod in contact with the thrust plate 38. In addition to the use of a retainer plate 44 other means may be used separately or in combination to hold the piston shoe in contact with the thrust plate. These additional means are shown in FIGURES 9-l5. FIGURES 9, l0 and 15 show a hydraulic arrangement whereby a jet of fluid under high pressure is employed to exert a constant force on the retainer plate. In FIGURE 9, fluid is pumped by any pump means 300 through a passage or series of passages 350 within housing section 314 and acts upon a hold-down plate or cap .348 which bears against retainer plate 344. As before, the housing is composed of two sections 312 and 314, the piston 352 (see FIGURE 9) rides within a bore in the barrel 358, and the thrust package includes the cage 336, the thrust member 338 and the support plate 332. As shown in FIGURE 15 the pumping means for the fluid within passages 350 is provided by a series of vanes or blades 354 formed in or mounted on the front end of the barrel 352. By this construction the speed of the barrel will propel the fluid into the passages independently of the pressure in the system. In FIGURE 10 the cap member 448 is provided with a series of passages 360 communicating with the passages 350 in the housing member 314. The passages 360 lead to enlarged chambers in the cap member 448 which house retainer elements. These retainer elements may take the form of pistons 450, as shown, or balls (not shown). Another manner by which the piston shoes are more rigidly held down is by the use of magnetic attraction forces (see FIGURES 11-14). In FIGURE 11 the cage 436 and cap member 448 are made of nonfcrrous material, whereas the piston rod or shoe 450 and the retainer plate 444 are made of ferrous material. The thrust plate is magnetized and serves to hold down the members 444 and 450.

fed from the duct 66 and delivered to the duct 64.

In another modification, as shown in FIGURE 12, the arrangement is identical to that of FIGURE 11 except that the thrust member 418 may be made of non-ferrous material if desired and a 1 pair of annular magnet rings 420 and 422 are employed to hold down the members 450 and 444. In still another arrangement, as shown in FIGURE 13, the cage 466 and cap member 468 are made of non-ferrous material, whereas the piston rod 480, retainer plate 464 and thrust plate 478 are made of ferrous materials. A ring magnet insert 470 is interposed in the cage 466 to create a magnetic path through plate 464, rod 480 and plate 478. In a further modification, see FIGURE 14, the construction is identical to that of FIGURE 13, except that the annular magnet 500 is provided with a carbon or bronze plate while in one portion of a revolution, the connecting rods taking turns in transmitting impulses to the retainer plate 44.

As may be readily seen, the connecting rods 50 are comparatively hort, resulting in a rigid structure which might be referred to as a stiff structure. The short connecting rod reduces bending movement therein, thereby reducing the whipping tendency that is found when long piston rods are used. Furthermore, the short connecting rods reduce the mass, thereby reducing the inertia effects and reducing the undesirable effects caused by centrifugal forces. The arrangement of the piston rods and the arrangement of the thrust package, together with the baiancing of the thrust forces by supplying fluid pressures counteracting the mechanical thrust, results in extreme economy of operation of the pump or motor, as the case may be. Furthermore, the thrust package, as explained above, results in economy in production, so that the pump or motor is economical to produce and economical to operate.

The cap 163 has a low pressure duct 64 and a high pressure duct 66, as shown in FIGURE 1. The ducts communicate with an opening 62, so as to either permit fluid to be fed into the pump through the low pressure duct 64 and delivered to the high pressure duct 66, or, in the case of the device being used as a motor, fluid is In either case, the fluid flow and the direction of rotation may be reversed.

In the normal construction of this type, it is necessary that some circumferential clearance, commonly called back lash, be included, in order to provide universal motion of the barrel to remain fully seated on the valve surface of the cap. This clearance must be adequate to allow for machine tolerances, alignment of bearings and deflections of all members under load. Therefore, the normal requirements present a difiicult problem of fulfilment, inasmuch as mating splines with no back lash are desired in order to obtain a smooth rotation, yet sufiicient back lash must be included to compensate for all misalignment factors. In order to provide for the optimum relationship between the back lash and misalignment (i.e. the tooth is crowned on its working faces), a crowned tooth on the male member 61 has been provided. This arrangement provides for maximum freedom of alignment with a minimum of back lash.

The following description of the operation of the device will be made as though it were a pump, recognizing, however, that the device will operate in the opposite sense if used as a motor. By driving the shaft 16, by any suitload on the rod face.

the thrust plate.

able power means, the shaft 18 will be driven through the splines at 20 so as to drive the barrel 58 through the splines 61 and 63. A reservoir of fluid for the pump is connected with the low pressure orifice or duct 64. As the barrel 58 rotates, the pistons 52 will be reciprocated, since the inclination of the retainer plate with respect to the plane normal to the axis of rotation of the barrel makes the distance between the retainer plate and barrel greater at one portion than another. During one-half of the revolution, some of the pistons 52 will move to the left, as viewed in FIGURE 2, so as to take in fluid from the low pressure or intake duct 64, and during the other half of the revolution, some of the pistons will move to the right so as to expel the fluid under high pressure to the high pressure outlet or duct 66.

Some of the fluid entering through the opening 62 is bled between the cylindrical bores 56 of the barrel 58 and the pistons 52 to obtain a viscous flow in the radial passageway 54 through the longitudinal passageway 55 of the piston 52. The fluid passing through the passageway in the first faced ball rod communicates with the passageway 46 and counterbore 41 in the thrust plate 38. The dimensions of the cylinder bores and piston rods are controlled, so as to obtain a capillary passageway. The undercut or counterbore 5711 (see FIG. 4) in the face 57 of the piston rod 56 is included in order to relieve the The counterbores can also be in the form of slots. Of course, these counterbores may be eliminated if desired. The controlled leakage past the piston rod reduces and alleviates any hammering, pounding or pulsations of the flat face 57 of the ball rod 50 on the thrust plate 38. Impedance of the oil flow through the capillary passage between the piston and cylinder will produce dampening of the passageway pulsation and vibrations. The result is that the device operates more smoothly and quite noiselessly, as compared to previous devices.

In a hydraulic pump of this type, the surface adjacent the plate 32 and thrust plate 38 require fine machine tolerances such as provided by lapping, or the like. Therefore, the housing is made in two parts and is split near Since the thrust plate must operate about an axis which is at an angle to the axis of the shaft 16 and shaft 18, the surfaces forming a seat for the thrust plate are machined in the housing at the same angle as the thrust plate. By making the housing in this manner, a much simpler method is provided for machining the angular surfaces.

The above construction incorporates the desirable features of reducing leakage past the piston, and reducing the vibratory forces within the wobble plate assembly. By properly designing and controlling the dimensions of the cylinder, the piston and the passageways through the pistons and the ball rod face along with the counterbores, that balancing can be achieved by which less frictional and vibrational forces are created. In this manner longer life expectancy of the pump is assured.

In the modification disclosed in FIGURE 6, a thrust plate 138 is used instead of the thrust plate 38. This thrust plate 138 is provided with a plurality of cylindrical cavities 146, only one of which has been shown, in each of which is mounted an element such as a ball 142, functioning as a piston. The portion of the cylindrical cavity 140a, so to speak above the ball 142, is filled with oil under pressure, biasing the ball against the plate 32. Thus, the balls 142 function as ball bearings, reducing friction.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this inventionvarious changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

What we claim is:

1. In a piston type pump or motor comprising a housing of separable axially arranged sections: a shaft extending axially of said housing and being rotatably mounted therein; a thrust package comprising a plurality of plates having flat surfaces nested within one housing section and clamped thereto by another housing section, the surfaces of the plates of said package being positioned at a working angle to the axis of said housing; said shaft extending through said thrust package; a barrel mounted on said shaft, said barrel being provided with a plurality of cylindrical bores; pistons mounted in said bores and universally jointed each to a piston rod, said pistons being displaceable within said bores by co-action of said rods with said thrust package upon rotation of said shaft; said thrust package providing means to take the pressure thrust of the pistons which rotate withthe barrel and further providing means for retracting the pistons which include retainer means comprising one of said plates which engages the piston rods to positively retain the same in sliding engagement with another of said-plates.

2. In a fluid pump or motor of the type having a plurality of piston-piston rod assemblies and a swash plate; the combination including a housing, said housing have two sections; a thrust package fitted within one housing section consisting of a plurality of superimposed flat plates and an annular cage surrounding at least some of the plates, one of said plates being the swash plate; retaining means positively holding the piston rods and swash plate in relatively sliding thrust engaging relationship; and means including the other housing section positioning said retaining means in fixed relationship to said housing.

3. The combination of claim 2, wherein the thrust package assembly comprises in combination; an annular retainer cap; a retainer plate provided with a plurality 'Of piston rod receiving openings; a swash plate provided with a plurality of passageways terminating in cavities; a back-up late and an annular cage enclosing said swash plate and retainer plate and being in turn held between said back-up plate and retainer cap by the mating of said housing sections.

4. A piston-type fluid pump or motor having a plurality of pistons displaceable in cylinders, and a plurality of rods forming sets of piston-piston rod assemblies, each rod being universally jointed to a piston at one end and having a surface at the other end, a thrust member, the surface at the other end of each said rod slidably bearing against the thrust member; a support surface for the thrust member; said thrust member having a surface which is in contact with said support surface and being further rovided with a plurality of through bores terminating in cavities on said surface which is in contact with said support surface; each piston-rod assembly having a passageway provided with a viscous flow path to provide fluid communication from a pressure chamber at one end of the piston to the rod bearing surface and thereby to a thrust member cavity and bore when the latter are in registration with a passageway, to obtain a fluid balance of the thrust member upon its support with minimum fiuid leakage therebetween; the bores and cavities in the thrust member are of a number in excess of she number of piston rods, with the distance between bore centers being slightly greater than the largest crosssectional dimension of the piston-rod assembly passageway so as to establish substantially constant communication between at least one of the thrust plate bores and piston-rod passageways and obtain a substantially constant fluid balance between the thrust member and its supporting surface for any given relative displacement of the rod on the thrust plate which is less than the distance between the rod cavities of two adjacent rods. 5. In a piston type pump or motor having a housing, in combination: a cavity within said housing; a rotating cylinder barrel mounted. within a portion of the cavity in said housing and having a, plurality of cylindrical i2 bores therein; piston-rod assemblies displaceable one within each of said cylindrical bores; an inclined thrust member within said cavity; each rod of said piston-rod assemblies having a face co-acting with a surface of the thrust member; a piston-rod retainer plate through which the piston rod assemblies pass; both said thrust member and plate being so arranged as to be freely rotatively mounted within said cavity in the housing and held against all radial displacement while capable of limited axial displacement; and means including said thrust member and retainer plate to positively retain said rods in sliding engagement with said thrust member, said means including a fluid passage arranged to conduct fluid under pressure and impinge same upon said retainer plate.

6; In a piston type pump or motor having a housing, in combination: a cavity within said housing; a rotating cylinder barrel mounted within a portion of the cavity in said housing and having a plurality of cylindrical bores therein; piston-rod assemblies displaceable one Within each of said cylindrical bores; an inclined thrust member within said cavity; each rod of said piston-rod assemblies having a face co-acting with a surface of the thrust member; a piston-rod retainer plate through which the piston-rod assemblies pass, both said thrust member and retainer plate being so arranged as to be freely rotatively mounted within said cavity in the housing and held against all radial displacement while capable of limited axial displacement; and means including said thrust member to positively retain said rods in sliding engagement with said thrust member, said means including magnetic means for attracting and holding said piston-rods to said thrust member.

7. In a fluid motor or pump, in combination: a barrel having a plurality of cylinders; a thrust member having its thrust surface angularly disposed with respect to said cylinders; a corresponding number of pistons forming piston-cylinder pairs, each piston being disposed within a cylinder and in engagement at one of its ends with said thrust surface, thereby effecting, upon relative rotation of said barrel and said thrust member, relative axial displacement of said pistons and cylinders, the other end of said pistons being periodically subjected to high fluid pressure; fluid fiow means for each of said piston-cylinder pairs establishing fluid flow communication interconnecting the high pressure area at said othgr end of each of said pistons to the thrust bearing portion at said one end thereof; fluid flow control means within each of said fluid flow means, including a viscous flow path formed by walls within said device, and portions of the walls of the viscous flow path being relatively displaceable with respect to one another throughout the duration of the pressure stroke for effecting, for substantially the duration of the pressure stroke of each of said pistons, a high resistance to fluid flow within said flow means, the resistance being of such magnitude as to cause a high average pressure drop, thereby minimizing leakage loss.

8. In a fluid motor or pump, in combination: a barrel having a plurality of cylinders; a thrust member having its thrust surface angularly disposed with respect to said cylinders; a corresponding number of pistons forming pistomcylinder pairs, each piston being disposed within a cylinder and in engagement at one of its ends with said thrust surface, thereby effecting, upon relative rotation of said barrel and said thrust member, relative axial displacement of said pistons and cylinders, the other end of said pistons being periodically subjected to high fluid pressure; fluid flow means for each of said piston-cylinder pairs establishing fluid flow communication interconnecting the high pressure area at said other end of each of said pistons to the thrust bearing portion at said one end thereof; fluid flow control means within each of said fluid flow means, including a viscous flow path for effecting, for substantially the duration of the pressure stroke of each of said pistons, a.

high resistance to fluid flow within said flow means, the resistance being of such magnitude as to cause a high average pressure drop, thereby minimizing leakage loss, said fiuid flow means further including means effecting a continuous wiping action upon the effective viscous flow path area throughout the duration of the pressure stroke.

9. In a piston type pump or motor having a housing, in combination: a cavity Within said housing; a rotating cylinder barrel mounted Within a portion of the cavity in said housing and having a plurality of cylindrical bores therein; piston-rod assemblies displaceable one within each of said cylindrical bores; an inclined thrust member within said cavity; each rod of said piston-rod assemblies having a face co-acting with a surface of the thrust member; a piston-rod retainer plate through which the piston-rod assemblies pass; both said retainer plate and thrust member being so mounted as to be restricted substantially to planar rotary movement within the housing cavity and being free to rotate relative to each other; and means to positively retain said rods in sliding engagement with said thrust member.

10. In a fluid motor or pump: a barrel having a plurality of cylinders; a thrust member having its thrust surface angularly disposed with respect to said cylinders; a corresponding plurality of pistons disposed one within each of said cylinders to form piston-cylinder pairs; a plurality of piston rods universally jointed at one end one to each of said pistons and in engagement with said thrust surface at their other ends for effecting, upon relative rotation of said barrel and said thrust member, relative axial displacement of said pistons and cylinders; the thrust surface engaging ends of the piston rods each having a suitable cavity to provide a predetermined contact area at the interface between it and the thrust member; the end of each piston opposite from its universal joint having an area which is periodically subjected to high fluid pressure; each of said pistons and rods having a communicating passageway extending at least partially therethrough to provide fluid communication from a pressure chamber adjacent the high pressure piston area to the cavity in the associated piston rod; said passageways each including a passage portion of fixed capillary dimension formed by the clearance between a surface portion of each piston and the bore of its cylinder for restricting the flow to laminar flow and for causing a relatively low rate of flow therethrough to obtain a low average pressure valve at said interface substantially throughout the entire pressure stroke of said pistons, thereby avoiding excessive leakage of fluid at the interface, said capillary passage portion remaining substantially fixed in size throughout the cycle of operation of said pump.

References Cited in the file of this patent UNITED STATES PATENTS 1,093,964 Andrews Apr. 21, 1914 1,710,567 Carey Apr. 23, 1929 2,313,407 Vickers et a1. Mar. 9, 1943 2,403,371 Ifield et a1. July 2, '1946 2,487,617 Tweedale Nov. 8, 1949 2,604,856 Henrichsen July '29, 1952 2,649,741 Henrichsen Aug. 25, 1953 2,699,123 Bonnette et a1 Ian. 11, 1955 2,709,339 Edelman et al May 3-1, 1955 2,757,612 Shaw Aug. 7, 1956 2,804,828 Grad Sept. 3, 1957 2,809,595 Adams et a1. Oct. 15, 1957 2,862,456 Bauer Dec. 2, 1958 FOREIGN PATENTS 602,978 France Ian. 5, 1926 539,637 Great Britain Sept. 18, 1941 604,168 Great Britain June 29, 1948 

1. IN A PISTON TYPE OR MOTOR COMPRISING A HOUSING OF SEPARABLE AXIALLY ARRANGED SECTIONS: A SHAFT EXTENDING AXIALLY OF SAID HOUSING AND BEING ROTATABLY MOUNTED THEREIN; A THRUST PACKAGE COMPRISING A PLURALITY OF PLATES HAVING FLAT SURFACES NESTED WITHIN ONE HOUSING SECTION AND CLAMPED THERETO BY ANOTHER HOUSING SECTION, THE SURFACES OF THE PLATES OF SAID PACKAGE BEING POSITIONED AT A WORK ING ANGLE TO THE AXIS OF SAID HOUSING; SAID SHAFT EXTENDING THROUGH SAID THRUST PACKAGE; A BARREL MOUNTED ON SAID SHAFT, SAID BARREL BEING PROVIDED WITH A PLURALITY OF CYLINDRICAL BORES; PISTONS MOUNTED IN SAID BORES AND UNIVERSALLY JOINTED EACH TO A PISTON ROD, SAID PISTONS BEING DISPLACEABLE WITHIN SAID BORES BY CO-ACTION OF SAID RODS WITH SAID THRUST PACKAGE UPON ROTATION OF SAID SHAFT; SAID THRUST PACKAGE PROVIDING MEANS TO TAKE THE PRESSURE THRUST OF THE PISTONS WHICH ROTATE WITH THE BARREL AND FURTHER 